E-stop wiring

[SPEEDRE]

I want to use the e-stop that came on my Grizzly mini mill over on my gantry mill. question , can I ? If so how do I wire it using Mach 2/3.

[Evodyne]

Originally Posted by SPEEDRE I want to use the e-stop that came on my Grizzly mini mill over on my gantry mill. question , can I ? If so how do I wire it using Mach 2/3.

Speedre,

Hi. My personal slant on an e-stop is that it needs to physically remove power to the device in question directly. In other words, it should kill the drives themselves so there is no possibility that the software might lock up in the "full speed ahead" mode when you press the e-stop. You can always tell the software you've pressed the e-stop in addition to killing the drives, but not in place of.

Consider the circuit in the attached picture. A relay is connected in a self-latching circuit. It starts out unlatched, and your drives are dead. Pressing the ARM button (a normally open, momentary contact pushbutton) energizes the relay R1 and closes all of the R1 contacts. One of these continues to keep the relay energised even after the ARM pushbutton is released. If any of the e-stop buttons E1 through E3 (you could have more or less) is pressed, they drop out the relay R1 and it contacts open, taking power off of the drives. Kickback diodes across the relay contacts prevent arcing that might destroy the contacts. Note that even if the e-stop button is pulled out/released, the circuit stays dead until intentionally rearmed via the ARM button. Relay contacts need to be rated for to handle the drives maximum current. Diodes need a PIV rating in excess of voltage applied to the drives and ideally would should be fast acting types like Schottky diodes. The second supplies voltage should match the relay coil voltage.

Evodyne

[rustyolddo]

The one problem with taking power off the drives is that it allows them to go into freewheel. In the case of a heavy mill head, the head could come crashing down.

An alternative is to take advantage of dynamic motor braking and short the leads of the motors together or thru a low value resistor with a "break before make" switch transition from power to stop. It can be done by simply modifying the posted circuit.

Another alternative that I've thought of but not tested is grounding all the step & direction control lines from the computer to the controller. That would keep the motors from free wheeling.

Some controller chips have a mode for E-Stop, and there are other schemes to keep from losing your position and rezeroing the maching. You can approach E-Stop as a last ditch all out emergentcy which can occur perhaps once a year, or as a more common occurance where you might have a tool crash or broken/jammed tool bit, loose clamp etc. I prefer this method as to the "nuclear" option as this will occur far more frequently.

[SPEEDRE]

Thanks for the informatiom but I haven't a clue what it all means. I am a complete donkey when it comes to electronical theorums and high end shematics. It may be hard on me to solve this issue as it is that I'm at a definate disadvantage here. Well guys I realy appreciate the help.

[Evodyne]

Originally Posted by SPEEDRE Thanks for the informatiom but I haven't a clue what it all means. I am a complete donkey when it comes to electronical theorums and high end shematics. It may be hard on me to solve this issue as it is that I'm at a definate disadvantage here. Well guys I realy appreciate the help.

Speedre,

Sorry-didn't mean to overwhelm you. It's really not that complicated. My post was how a typical e-stop circuit might work, regardless of the device. rustyolddo correctly mentioned some problems with my generic approach when applied specifically to CNC: taking power off the drives wouldn't necessarily stop movement from coasting or backdriving.

Really what would be best would be a little more information about your setup-you mentioned Mach 2, but what kind of drives, speed reduction, motion hardware (ballsecrew? lead screws? etc). I'm guessing if you let the group know waht you've got that collectively we can give you more direct and understandable advice. Give it a shot!

And rustyolddo, thanks for the comments. I'm new to the whole CNC thing myself and hadn't taken those factors into account. Good job!

Lance

[SPEEDRE]

Well guys I need to know where it gets wired to and from. If I asked this, if I wire all the motor wires to a terminal strip, pass them to the e-stop switch, then pass them on to the controler what would happen? If I push the button will it all stop? Does this make any sense???

[carlnpa]

Some low tech ideas.
Don't bother trying to isolate the motors. Run your driver power supply and spindle on a terminal switch with an on/off button. Mount close to hand.
You could also run power to the spindle and power supply through an e-stop switch like those found on the mini-lathes either on a pendant or fixed location like this one. Just wire it like a light switch.
http://www.littlemachineshop.com/pro...ProductID=1332

[SPEEDRE]

Thanks Carlnpa, that's exactly the one I would like to use but, again, how and where to attatch the wires? I do like the idea of a master kill switch but one question beggs here, if I cut the power to the spindle it keeps moving, the carriage and all, right.?